This invention relates to linear reciprocating motors, and preferably to motors of this type wherein a piston reciprocates within a cylinder under the control of pressurized hydraulic oil. More particularly, the invention relates to an improved reciprocating valve for controlling the motion of such a piston.
The construction and operation of reciprocating motors has long been known in the prior art, such motors being designed to permit pressurized hydraulic oil first into one end of a cylinder to force a piston to linearly move within the cylinder, and then into the other end of the cylinder to cause the piston to reciprocate in the other direction. The control of oil flow into such a motor is accomplished by a reciprocation valve and a trip rod or lever connected between the valve and the piston. The trip rod is designed so as to be contacted by the piston at both extremes of piston reciprocation, and to cause movement thereby to toggle the reciprocation valve into one of two valving positions. The selective toggling of the reciprocation valve causes a change in oil flow into the cylinder and redirects the oil pressure forces to reverse the axial piston motion within the cylinder.
A principal problem in the design of such reciprocating motors has been the reciprocation valve. The valve must distinctly occupy one of two valve porting positions, and must move to each of the two positions immediately upon actuation of the toggling member. Care must be used in examining worst case operating conditions to ensure that no valve "dead spot" occurs which would otherwise permit the valve to position itself intermediate the two operational positions. Various detent mechanisms have been used to provide positive valve positioning, and positive valve stops have been incorporated into the design to prevent the valve from moving beyond its designed stop positions. Since the valve controls the flow of pressurized hydraulic oil a good seal must be provided within the valve to prevent oil leakage, even after millions of cycles of usage.
To accomplish the design requirements of such a reciprocation valve the prior art has utilized a spool valve construction, usually in combination with a spring-loaded detent mechanism for positively stopping spool valve movement in either of two positions. For example, Swedish Pat. No. 63691, issued on Sept. 13, 1927, shows the typical spool valve construction commonly found in reciprocating motors of this type. U.S. Pat. No. 4,079,660, issued Mar. 21, 1978, shows a variation of spool valve construction. In such prior art designs a generally cylindrically shaped spool is slidable within a cylinder into flow communication with various ports. The spool itself is ported to provide an oil flow communication path, and the spool is typically actuated by a rod which comes into contact with the piston at or near the extreme piston travel positions. Positive valve stops are usually provided to ensure that the spool valve does not travel beyond either of its stop positions. In such valves the spool is constructed of a relatively high mass material, sufficient to withstand the porting of pressurized oil and the repetitive mechanical contact with stops. This contact produces an audible noise each time the valve reciprocates, and adds to the overall noise level of operation of such motors. Because of the relatively high mass of the spool valve the toggling mechanism must also be of sturdy construction, all of which adds to the cost of design and manufacture of such valves.